Baffled thermoclines in thermodynamic generation cycle systems

ABSTRACT

Solid-state thermoclines with internal baffle structures are in used in place of heat exchangers in a closed thermodynamic cycle power generation or energy storage system, such as a closed Brayton cycle system. The baffles limit the conductive and/or radiative transfer of heat between a solid thermal medium within different zones defined by the baffle structures.

CROSS REFERENCE TO RELATED APPLICATION

This utility application is a Continuation of co-pending U.S. patentapplication No. 15/392,542, filed Dec. 28, 2016, the contents of whichare incorporated herein by reference in their entirety, including butnot limited to those portions concerning thermodynamic cycle powerand/or energy storage.

BACKGROUND

In a heat engine or heat pump, a heat exchanger may be employed totransfer heat between a thermal storage medium and a working fluid foruse with turbomachinery. The heat engine may be reversible, e.g., it mayalso be a heat pump, and the working fluid and heat exchanger may beused to transfer heat or cold to a plurality of thermal stores.

SUMMARY

In a closed thermodynamic cycle power generation or energy storagesystem, such as a reversible Brayton cycle system, a pressure vesselcontaining a solid thermal medium in a thermocline arrangement may beused as a parallel flow or counter-flow direct-contact heat exchanger inplace of a fluid-to-fluid heat exchangers. The thermocline may bemaintained through the use of internal baffles which segregate the solidthermal medium into zones within the pressure vessel.

Example thermocline vessels may include an insulated pressure vessel, aninlet for receiving a working fluid at non-atmospheric pressure, anoutlet for dispatching the working fluid at non-atmospheric pressure, asolid thermal medium within the insulated pressure vessel and havingporosity sufficient to allow the working fluid to flow through the solidthermal medium, a plurality of baffle structures defining a plurality ofzones within the insulated pressure vessel, wherein the solid thermalmedium is located within the plurality of zones, wherein each bafflestructure is configured to limit direct transfer of heat between thesolid thermal medium in different zones, one or more fluid channelsconfigured to channel the working fluid past the baffles and in contactwith the solid thermal medium.

Example systems may include a compressor, a first thermocline vesselcomprising a plurality of zones of a solid thermal medium defined bybaffle structures in the interior of the first thermocline vessel,wherein each baffle structure is configured to limit direct transfer ofheat between the solid thermal medium in different zones, a turbine, anda working fluid circulating, in order, through (i) the compressor, (ii)the first thermocline vessel and the solid thermal medium in theinterior of the first thermocline vessel, and (iii) the turbine, whereinthe solid thermal medium within a first zone proximate to an inlet ofthe working fluid to the first thermocline vessel is at a firsttemperature, and wherein the solid thermal medium within a second zoneproximate to an outlet of the working fluid from the first thermoclinevessel is at a second temperature higher than the first temperature.

Example energy generation systems may include a generator configured toreceive mechanical energy and generate electrical energy a workingfluid, a compressor configured to compress the working fluid, a turbineconfigured to convert expansion of the working fluid within the turbineinto mechanical energy, wherein the turbine is mechanically coupled tothe compressor and is configured to transmit a portion of the mechanicalenergy through the mechanical coupling to drive the compressor, arecuperative heat exchanger configured to thermally contact workingfluid exiting the compressor with working fluid exiting the turbine; acooling tower configured to eject to the atmosphere heat carried by theworking fluid, a hot-side thermocline vessel comprising a plurality ofzones of a first solid thermal medium defined by baffle structures inthe interior of the first thermocline vessel, wherein each bafflestructure is configured to limit direct transfer of heat between thefirst solid thermal medium in different zones, and a cold-sidethermocline vessel comprising a plurality of zones of a second solidthermal medium defined by baffle structures in the interior of the firstthermocline vessel, wherein each baffle structure is configured to limitdirect transfer of heat between the second solid thermal medium indifferent zones, wherein the working fluid circulates, in order, through(i) the compressor, (ii) the recuperative heat exchanger, (iii) thehot-side thermocline vessel and the first solid thermal medium in theinterior of the hot-side thermocline vessel, (iv) the turbine, (v) therecuperative heat exchanger, (vi) the cooling tower, and (vii) thecold-side thermocline vessel and the second solid thermal medium in theinterior of the cold-side thermocline vessel.

These as well as other aspects, advantages, and alternatives, willbecome apparent to those of ordinary skill in the art by reading thefollowing detailed description, with reference where appropriate to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow diagram of working fluid and heat storagemedia of a thermal system in a charge/heat pump mode.

FIG. 2 is a schematic flow diagram of working fluid and heat storagemedia of a thermal system in a discharge/heat engine mode.

FIG. 3A is a schematic pressure and temperature diagram of the workingfluid as it undergoes the charge cycle in FIG. 1.

FIG. 3B is a schematic pressure and temperature diagram of the workingfluid as it undergoes the discharge cycle in FIG. 2.

FIG. 4 is a schematic flow diagram of working fluid and heat storagemedia of a thermal system with a gas-gas heat exchanger for the workingfluid in a charge/heat pump mode.

FIG. 5 is a schematic flow diagram of working fluid and heat storagemedia of a thermal system with a gas-gas heat exchanger for the workingfluid in a discharge/heat engine mode.

FIG. 6A is a schematic pressure and temperature diagram of the workingfluid as it undergoes the charge cycle in FIG. 4.

FIG. 6B is a schematic pressure and temperature diagram of the workingfluid as it undergoes the discharge cycle in FIG. 5.

FIG. 7 illustrates a schematic flow diagram according to an exampleembodiment.

FIG. 8 illustrates a schematic arrangement, in cut-away view, of abaffled thermocline pressure vessel according to an example embodiment.

FIG. 9 illustrates a schematic arrangement, in cut-away view, of abaffled thermocline pressure vessel according to an example embodiment.

FIG. 10 illustrates a schematic arrangement, in cut-away view, of abaffled thermocline pressure vessel according to an example embodiment.

FIG. 11 illustrates a schematic arrangement, in cut-away view, of abaffled thermocline vessel with a runner, according to an exampleembodiment.

FIG. 12 illustrates an example embodiment of a baffle structures insidea thermocline pressure vessel.

FIG. 13 illustrates an example embodiment of a baffle structures insidea thermocline pressure vessel.

FIG. 14 illustrates an example embodiment of a baffle structures insidea thermocline pressure vessel.

FIG. 15 illustrates an example embodiment of a baffle structures insidea thermocline pressure vessel.

DETAILED DESCRIPTION

Example methods and systems are described herein. It should beunderstood that the words “example” and/or “exemplary” are used hereinto mean “serving as an example, instance, or illustration.” Anyembodiment or feature described herein as being an “example” or“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or features. The example embodimentsdescribed herein are not meant to be limiting. It will be readilyunderstood that certain aspects of the disclosed systems and methods canbe arranged and combined in a wide variety of different configurations,all of which are contemplated herein.

I. Overview

Reversible heat engines may use one or more solid thermal storagemediums to transfer heat to or from a working fluid. A solid thermalstorage medium may be contained within a thermocline vessel where thesolid thermal storage medium exists in a thermocline state with atemperature gradient across the medium. Disclosed herein are baffledthermocline vessels that may be used to help beneficially maintain thattemperature gradient. An example reversible closed heat engine in whichbaffled thermocline vessels may be implemented is a Brayton enginesystem. A Brayton engine system may use a generator/motor connected to aturbine and a compressor, where the turbomachinery acts on a workingfluid circulating in the system. Non-comprehensive examples of workingfluids include air, argon, carbon dioxide, or gaseous mixtures. ABrayton system may have a hot side and a cold side. Each side mayinclude a heat exchanger vessel containing a solid thermal medium Thesolid thermal medium may take many forms, including but not limited to,dirt, rock, gravel, sand, clay, metal, metal oxide, refractory material,refractory metal, ceramic, cermet, alumina, silica, magnesia, zirconia,silicon carbide, titanium carbide, tantalum carbide, chromium carbide,niobium carbide, zirconium carbide, molybdenum disilicide, calciumoxide, chromite, dolomite, magnesite, quartzite, aluminum silicate,tungsten, molybdenum, niobium, tantalum, rhenium, beryllium, andcombinations thereof. The solid thermal medium for use in cold systemsmay further include water ice, and/or other solid forms of common roomtemperature liquids. Preferably, the solid medium is structurally stableat high or low temperature, of uniform shape and/or size, and shapedsuch that a bolus of the solid medium includes gaps to allow a workingfluid to flow through the bolus. For example, for refractory materialsit may be preferable to utilize larges slabs, stackable bricks, platonicsolids, spheres, cylinders, or other shapes that can be stacked and/orarranged to allow gaps between individual units of the solid medium. Formetal, metal oxides, or ceramics it may be preferable to use thoseshapes or fabrics or meshes that consist entirely or partially of themetal, metal oxide, or ceramic, where the fabric or mesh has a porositysufficient to allow passage of a working fluid through the solid medium.

The hot-side solid thermal medium may reach temperatures over 600° C.and, if the heat exchanger vessel operates as direct contact between theworking fluid and the hot-side solid thermal medium, the pressure may beover 100 bars. Similarly, cold-side thermal medium can go below −70° C.and be at or near vacuum state in the heat exchanger.

It may be desirable to configure a Brayton cycle heat exchanger vesselas a counter-flow heat exchanger to maximize efficiency of the thermalcycle. Preferably, this may be implemented via a thermocline, ortemperature gradient within the heat exchanger vessel, wherein the heatexchanger vessel may include a pressure vessel. For a hot-side heatexchanger vessel in a discharging Brayton cycle, the entering workingfluid preferably contacts the coldest solid thermal medium at theentrance to the heat exchanger vessel and contacts the hottest solidthermal medium at the exit to the heat exchanger vessel. For a cold-sideheat exchanger in a discharging Brayton cycle, the entering workingfluid preferably contacts the hottest solid thermal medium at theentrance to the heat exchanger and contacts the coldest solid thermalmedium at the exit to the heat exchanger. The contact between theworking fluid and the solid thermal medium may be direct contact orindirect thermal contact depending on the configuration. In a chargingBrayton cycle, the contacting order would preferably be reversed.

Disadvantageously, the solid thermal medium in a thermocline arrangementwithin a heat exchanger vessel may conduct, convect, and/or radiate heatfrom hot portions of the solid thermal medium to cold portions untilequilibrium is reached throughout the solid thermal medium.Non-beneficial direct transfer of heat through the solid thermal mediummay include conductive heat transfer from a portion of the solid thermalmedium in direct contact with another portion of the solid thermalmedium, or in contact through a thermal transfer medium such as anuninsulated and/or conductive surface of the heat exchanger vessel.Direct transfer of heat may also include radiative (or emissive) heattransfer from a portion of solid thermal medium to another portion ofsolid thermal medium, where the two portions are not in direct contact.For purposes herein, direct transfer of heat does not include heattransfer by means of a working fluid passing over solid thermal medium,where the working fluid carries heat from one portion of the solidthermal medium to another portion. Prior to thermal equilibrium,conductive and/or radiative heat transfer through or among the solidthermal medium will reduce the maximum temperature difference across thethermocline and potentially reduce overall thermal efficiency of athermodynamic (e.g. Brayton) cycle employing a direct contactthermocline heat exchanger.

To mitigate direct heat transfer within the solid thermal storagemedium, one or more baffle structures may be included in the heatexchanger vessel to create zones within the heat exchanger vessel. Eachzone may contain a portion of the total quantity of the solid thermalmedium in the heat exchanger vessel and the baffle structures may limitdirect transfer of heat between the solid thermal medium in one zone tothe solid thermal medium in a different zone.

The baffle structures may take forms configured to limit direct transferof heat between the solid thermal medium in different zones, while stillallowing a working fluid to reach the solid thermal medium while flowingthrough the heat exchanger. For example, a baffle structure may be aninsulated wall extending partially across the heat exchanger, leaving aspace for working fluid flow between an end of the insulated wall and aninterior wall of the pressure vessel. As another example, a bafflestructure may be an insulated wall extending completely across the heatexchanger. The wall may include fluid channels through the wall thatallow a working fluid to flow through the wall. The working fluid mayflow throughout the heat exchanger or may be constrained to runners thattraverse the heat exchanger and are in thermal contact with the solidthermal medium.

The fluid channels may be sized or located to limit or prevent themovement of the solid thermal medium through the fluid channels.Alternatively or additionally, the fluid channels may be sized, located,and/or shaped to limit the effect of radiative heat transfer. Forexample, a fluid channel may be angled or convoluted in form such thatthere is no, or limited, line-of-sight between the solid thermal mediumon one side of the fluid channel and the solid thermal medium on theother side of the fluid channel. Similarly, another baffle structure maybe a perforated material extending across the heat exchanger. Theperforated material may be physically separated from the solid thermalmedium to prevent or limit conductive heat transfer and the perforationsmay act similarly to the wall-based fluid channels described above.Other baffle structures may include insulated chambers within the heatexchanger that each contain the solid thermal medium and a plurality offluid channels that allow a working fluid to enter the chamber, contactthe solid thermal medium directly or through runners, and exit thechamber.

II. Illustrative Reversible Heat Engine

Systems and devices in which example embodiments may be implemented willnow be described in greater detail. However, an example system may alsobe implemented in or take the form of other devices, without departingfrom the scope of the invention.

An aspect of the disclosure relates to thermal systems operating onthermal storage cycles. In some examples, the cycles allow electricityto be stored as heat (e.g., in the form of a temperature differential)and then converted back to mechanical work and ultimately electricitythrough the use of at least two pieces of turbomachinery (a compressorand a turbine), and a generator. The compressor consumes work and raisesthe temperature and pressure of a working fluid (WF). The turbineproduces work and lowers the temperature and pressure of the workingfluid. In example systems, more than one compressor and/or more than oneturbine may be used. The compressors may be arranged in series or inparallel. The turbines may be arranged in series or in parallel.

FIGS. 1 and 2 are schematic flow diagrams of working fluid and heatstorage medium of an example thermal system in a charge/heat pump modeand in a discharge/heat engine mode, respectively. The system may beidealized for simplicity of explanation so that there are no losses(i.e., entropy generation) in either the turbomachinery or heatexchangers. The system can include a working fluid (e.g., argon gas)flowing in a closed cycle between a compressor 1, a hot side heatexchanger 2, a turbine 3 and a cold side heat exchanger 4. Fluid flowpaths/directions for the working fluid (e.g., a gas), a hot side thermalstorage (HTS) medium 21 (e.g., a low viscosity liquid or a solid medium)and a cold side thermal storage (CTS) medium 22 (e.g., a low viscosityliquid or a solid medium, which may be different from the HTS medium)are indicated by arrows. The heat exchangers 2 and 4 exchangers mayincorporate, for example, conventional liquid-to-gas exchange for liquidthermal storage media (e.g., tube-and-shell exchangers or plateexchanger) and solid-to-gas exchange (e.g., direct contact) for thesolid thermal medium and may require pumping and/or conveyancemechanisms for the media.

FIGS. 3A and 3B are schematic pressure and temperature diagrams of theworking fluid as it undergoes the charge cycles in FIGS. 1 and 2,respectively, once again simplified in the approximation of no entropygeneration. Normalized pressure is shown on the y-axes and temperatureis shown on the x-axes. The direction of processes taking place duringthe cycles is indicated with arrows, and the individual processes takingplace in the compressor 1, the hot side CFX 2, the turbine 3 and thecold side CFX 4 are indicated on the diagram with their respectivecircled numerals.

The heat exchangers 2 and 4 can be configured as counter-flow heatexchangers (CFXs), where the working fluid flows in one direction andthe substance it is exchanging heat with is flowing or moving or has atemperature gradient in the opposite direction. In an ideal counter-flowheat exchanger with correctly matched flows (i.e., balanced capacitiesor capacity flow rates or thermocline gradient), the temperatures of theworking fluid and thermal storage medium flip (i.e., the counter-flowheat exchanger can have unity effectiveness).

The counter-flow heat exchangers 2 and 4 can be designed and/or operatedto reduce entropy generation in the heat exchangers to negligible levelscompared to entropy generation associated with other system componentsand/or processes (e.g., compressor and/or turbine entropy generation).In some cases, the system may be operated such that entropy generationin the system is minimized. For example, the system may be operated suchthat entropy generation associated with heat storage units is minimized.In some cases, a temperature difference between fluid or solid elementsexchanging heat can be controlled during operation such that entropygeneration in hot side and cold side heat storage units is minimized. Insome instances, the entropy generated in the hot side and cold side heatstorage units is negligible when compared to the entropy generated bythe compressor, the turbine, or both the compressor and the turbine. Insome instances, entropy generation associated with heat transfer in theheat exchangers 2 and 4 and/or entropy generation associated withoperation of the hot side storage unit, the cold side storage unit orboth the hot side and cold side storage units can be less than about50%, less than about 25%, less than about 20%, less than about 15%, lessthan about 10%, less than about 5%, less than about 4%, less than about3%, less than about 2%, or less than about 1% of the total entropygenerated within the system (e.g., entropy generated by the compressor1, the hot side heat exchanger 2, the turbine 3, the cold side heatexchanger 4 and/or other components described herein, such as, forexample, a recuperator). For example, entropy generation can be reducedor minimized if the two substances exchanging heat do so at a localtemperature differential ΔT→0 (i.e., when the temperature differencebetween any two fluid or solid media elements that are in close thermalcontact in the heat exchanger is small). In some examples, thetemperature differential ΔT between any two fluid or solid mediaelements that are in close thermal contact may be less than about 300Kelvin (K), less than about 200 K, less than about 100 K, less thanabout 75 K, less than about 50 K, less than about 40 K, less than about30 K, less than about 20 K, less than about 10 K, less than about 5 K,less than about 3 K, less than about 2 K, or less than about 1 K. Inanother example, entropy generation associated with pressure drop can bereduced or minimized by suitable design. In some examples, the heatexchange process can take place at a constant or near-constant pressure.Alternatively, a non-negligible pressure drop may be experienced by theworking fluid and/or one or more thermal storage media during passagethrough a heat exchanger. Pressure drop in heat exchangers may becontrolled (e.g., reduced or minimized) through suitable heat exchangerdesign. In some examples, the pressure drop across each heat exchangermay be less than about 20% of inlet pressure, less than about 10% ofinlet pressure, less than about 5% of inlet pressure, less than about 3%of inlet pressure, less than about 2% of inlet pressure, less than about1% of inlet pressure, less than about 0.5% of inlet pressure, less thanabout 0.25% of inlet pressure, or less than about 0.1% of inletpressure.

Upon entering the heat exchanger 2, the temperature of the working fluidcan either increase (taking heat from the HTS medium 21, correspondingto the discharge mode in FIGS. 2 and 3B) or decrease (giving heat to theHTS medium 21, corresponding to the charge mode in FIGS. 1 and 3A),depending on the temperature of the HTS medium in the heat exchangerrelative to the temperature of the working fluid. Similarly, uponentering the heat exchanger 4, the temperature of the working fluid caneither increase (taking heat from the CTS medium 22, corresponding tothe charge mode in FIGS. 1 and 3A) or decrease (giving heat to the CTSmedium 22, corresponding to the discharge mode in FIGS. 2 and 3B),depending on the temperature of the CTS medium in the heat exchangerrelative to the temperature of the working fluid.

As described in more detail with reference to the charge mode in FIGS. 1and 3A, the heat addition process in the cold side CFX 4 can take placeover a different range of temperatures than the heat removal process inthe hot side CFX 2. Similarly, in the discharge mode in FIGS. 2 and 3B,the heat rejection process in the cold side CFX 4 can take place over adifferent range of temperatures than the heat addition process in thehot side CFX 2. At least a portion of the temperature ranges of the hotside and cold side heat exchange processes may overlap during charge,during discharge, or during both charge and discharge.

As used herein, the temperatures T₀, T₁, T₀ ⁺ and T₁ ⁺ are so namedbecause T₀ ³⁰ , T₁ ⁺ are the temperatures achieved at the exit of acompressor with a given compression ratio r, adiabatic efficiency η_(c)and inlet temperatures of T₀, T₁ respectively. The examples in FIGS. 1,2, 3A and 3B can be idealized examples where η_(c)=1 and where adiabaticefficiency of the turbine η_(t) also has the value η_(t)=1.

With reference to the charge mode shown in FIGS. 1 and 3A, the workingfluid can enter the compressor 1 at position 30 at a pressure P and atemperature T (e.g., at T₁, P₂). As the working fluid passes through thecompressor, work W₁ is consumed by the compressor to increase thepressure and temperature of the working fluid (e.g., to T₁ ⁺, P₁), asindicated by P↑ and T↑ at position 31. In the charge mode, thetemperature T₁ ⁺ of the working fluid exiting the compressor andentering the hot side CFX 2 at position 31 is higher than thetemperature of the HTS medium 21 entering the hot side CFX 2 at position32 from a second hot side thermal storage tank 7 at a temperature T₀ ⁺(i.e., T₀ ⁺<T₁ ⁺). As these working fluid and thermal medium pass inthermal contact with each other in the heat exchanger, the workingfluid's temperature decreases as it moves from position 31 to position34, giving off heat Q₁ to the HTS medium, while the temperature of theHTS medium in turn increases as it moves from position 32 to position33, absorbing heat Q₁ from the working fluid. In an example, the workingfluid exits the hot side CFX 2 at position 34 at the temperature T₀ ⁺and the HTS medium exits the hot side CFX 2 at position 33 into a firsthot side thermal storage tank 6 at the temperature T₁ ⁺. The heatexchange process can take place at a constant or near-constant pressuresuch that the working fluid exits the hot side CFX 2 at position 34 at alower temperature but same pressure P₁, as indicated by P and T↓ atposition 34. Similarly, the temperature of the HTS medium 21 increasesin the hot side CFX 2, while its pressure can remain constant ornear-constant.

Upon exiting the hot side CFX 2 at position 34 (e.g., at T₀ ⁺, P₁), theworking fluid undergoes expansion in the turbine 3 before exiting theturbine at position 35. During the expansion, the pressure andtemperature of the working fluid decrease (e.g., to T₀, P₂), asindicated by P↓ and T↓ at position 35. The magnitude of work W₂generated by the turbine depends on the enthalpy of the working fluidentering the turbine and the degree of expansion. In the charge mode,heat is removed from the working fluid between positions 31 and 34 (inthe hot side CFX 2) and the working fluid is expanded back to thepressure at which it initially entered the compressor at position 30(e.g., P₂). The compression ratio (e.g., P₁/P₂) in the compressor 1being equal to the expansion ratio in the turbine 3, and the enthalpy ofthe gas entering the turbine being lower than the enthalpy of the gasexiting the compressor, the work W₂ generated by the turbine 3 issmaller than the work W₁ consumed by the compressor 1 (i.e., W₂<W₁).

Because heat was taken out of the working fluid in the hot side CFX 2,the temperature T₀ at which the working fluid exits the turbine atposition 35 is lower than the temperature T₁ at which the working fluidinitially entered the compressor at position 30. To close the cycle(i.e., to return the pressure and temperature of the working fluid totheir initial values T₁, P₂ at position 30), heat Q₂ is added to theworking fluid from the CTS medium 22 in the cold side CFX 4 betweenpositions 35 and 30 (i.e., between the turbine 3 and the compressor 1).In an example, the CTS medium 22 enters the cold side CFX 4 at position36 from a first cold side thermal storage tank 8 at the temperature T₁and exits the cold side CFX 4 at position 37 into a second cold sidethermal storage tank 9 at the temperature T₀, while the working fluidenters the cold side CFX 4 at position 35 at the temperature T₀ andexits the cold side CFX 4 at position 30 at the temperature T₁. Again,the heat exchange process can take place at a constant or near-constantpressure such that the working fluid exits the cold side CFX 2 atposition 30 at a higher temperature but same pressure P₂, as indicatedby P and T↑ at position 30. Similarly, the temperature of the CTS medium22 decreases in the cold side CFX 2, while its pressure can remainconstant or near-constant.

During charge, the heat Q₂ is removed from the CTS medium and the heatQ₁ is added to the HTS medium, wherein Q₁>Q₂. A net amount of work(W₁−W₂) is consumed, since the work W₁ used by the compressor is greaterthan the work W₂ generated by the turbine. A device that consumes workwhile moving heat from a cold body or thermal storage medium to a hotbody or thermal storage medium may be considered a heat pump; thus, thethermal system in the charge mode may operate as a heat pump.

In an example, the discharge mode shown in FIGS. 2 and 3B can differfrom the charge mode shown in FIGS. 1 and 3A in the temperatures of thethermal storage media being introduced into the heat exchangers. Thetemperature at which the HTS medium enters the hot side CFX 2 atposition 32 is T₁ ⁺ instead of T₀ ⁺, and the temperature of the CTSmedium entering the cold side CFX 4 at position 36 is T₀ instead of T₁.During discharge, the working fluid enters the compressor at position 30at T₀ and P₂, exits the compressor at position 31 at T₀ ⁺<T₁ ⁺ and P₁,absorbs heat from the HTS medium in the hot side CFX 2, enters theturbine 3 at position 34 at T₁ ⁺ and P₁, exits the turbine at position35 at T₁>T₀ and P₂, and finally rejects heat to the CTS medium in thecold side CFX 4, returning to its initial state at position 30 at T₀ andP₂.

The HTS medium at temperature T₁ ⁺ can be stored in a first hot sidethermal storage tank 6, the HTS medium at temperature T₀ ⁺ can be storedin a second hot side thermal storage tank 7, the CTS medium attemperature T₁ can be stored in a first cold side thermal storage tank8, and the CTS medium at temperature T₀ can be stored in a second coldside thermal storage tank 9 during both charge and discharge modes. Inone implementation, the inlet temperature of the HTS medium at position32 can be switched between T₁ ⁺ and T₀ ⁺ by switching between tanks 6and 7, respectively. Similarly, the inlet temperature of the CTS mediumat position 36 can be switched between T₁ and T₀ by switching betweentanks 8 and 9, respectively. Switching between tanks can be achieved byincluding a valve or a system of valves, or a conveyance system or agroup of conveyance systems, for switching connections between the hotside heat exchanger 2 and the hot side tanks 6 and 7, and/or between thecold side heat exchanger 4 and the cold side tanks 8 and 9 as needed forthe charge and discharge modes. In some implementations, connections maybe switched on the working fluid side instead, while the connections ofstorage tanks 6, 7, 8 and 9 to the heat exchangers 2 and 4 remainstatic. In some examples, flow paths and connections to the heatexchangers may depend on the design (e.g., shell-and-tube ordirect-contact) of each heat exchanger. In some implementations, one ormore valves or conveyance systems can be used to switch the direction ofboth the working fluid and the heat storage media through thecounter-flow heat exchanger on charge and discharge. Such configurationsmay be used, for example, due to high thermal storage capacities of theheat exchanger component, to decrease or eliminate temperaturetransients, or a combination thereof. In some implementations, one ormore valves or conveyance systems can be used to switch the direction ofonly the working fluid, while the direction of the HTS or CTS can bechanged by changing the direction of pumping or conveyance, therebymaintaining the counter-flow configuration. In some implementations,different valve configurations or conveyance systems may be used for theHTS and the CTS. Further, any combination of the valve or conveyanceconfigurations herein may be used. For example, the system may beconfigured to operate using different valve or conveyance configurationsin different situations (e.g., depending on system operatingconditions).

In the discharge mode shown in FIGS. 2 and 3B, the working fluid canenter the compressor 1 at position 30 at a pressure P and a temperatureT (e.g., at T₀, P₂). As the working fluid passes through the compressor,work W₁ is consumed by the compressor to increase the pressure andtemperature of the working fluid (e.g., to T₀ ⁺, P₁), as indicated by P↑and T↑ at position 31. In the discharge mode, the temperature T₀ ⁺ ofthe working fluid exiting the compressor and entering the hot side CFX 2at position 31 is lower than the temperature of the HTS medium 21entering the hot side CFX 2 at position 32 from a first hot side thermalstorage tank 6 at a temperature T₁ ⁺ (i.e., T₀ ⁺<T₁ ⁺). As these twofluids pass in thermal contact with each other in the heat exchanger,the working fluid's temperature increases as it moves from position 31position 34, absorbing heat Q₁ from the HTS medium, while thetemperature of the HTS medium in turn decreases as it moves fromposition 32 to position 33, giving off heat Q₁ to the working fluid. Inan example, the working fluid exits the hot side CFX 2 at position 34 atthe temperature T₁ ⁺ and the HTS medium exits the hot side CFX 2 atposition 33 into the second hot side thermal storage tank 7 at thetemperature T₀ ⁺. The heat exchange process can take place at a constantor near-constant pressure such that the working fluid exits the hot sideCFX 2 at position 34 at a higher temperature but same pressure P₁, asindicated by P and T↑ at position 34. Similarly, the temperature of theHTS medium 21 decreases in the hot side CFX 2, while its pressure canremain constant or near-constant.

Upon exiting the hot side CFX 2 at position 34 (e.g., at T₁ ⁺, P₁), theworking fluid undergoes expansion in the turbine 3 before exiting theturbine at position 35. During the expansion, the pressure andtemperature of the working fluid decrease (e.g., to T₁, P₂), asindicated by P↓ and T↓ at position 35. The magnitude of work W₂generated by the turbine depends on the enthalpy of the working fluidentering the turbine and the degree of expansion. In the discharge mode,heat is added to the working fluid between positions 31 and 34 (in thehot side CFX 2) and the working fluid is expanded back to the pressureat which it initially entered the compressor at position 30 (e.g., P₂).The compression ratio (e.g., P₁/P₂) in the compressor 1 being equal tothe expansion ratio in the turbine 3, and the enthalpy of the gasentering the turbine being higher than the enthalpy of the gas exitingthe compressor, the work W₂ generated by the turbine 3 is greater thanthe work W₁ consumed by the compressor 1 (i.e., W₂>W₁).

Because heat was added to the working fluid in the hot side CFX 2, thetemperature T₁ at which the working fluid exits the turbine at position35 is higher than the temperature T₀ at which the working fluidinitially entered the compressor at position 30. To close the cycle(i.e., to return the pressure and temperature of the working fluid totheir initial values T₀, P₂ at position 30), heat Q₂ is rejected by theworking fluid to the CTS medium 22 in the cold side CFX 4 betweenpositions 35 and 30 (i.e., between the turbine 3 and the compressor 1).The CTS medium 22 enters the cold side CFX 4 at position 36 from asecond cold side thermal storage tank 9 at the temperature T₀ and exitsthe cold side CFX 4 at position 37 into a first cold side thermalstorage tank 8 at the temperature T₁, while the working fluid enters thecold side CFX 4 at position 35 at the temperature T₁ and exits the coldside CFX 4 at position 30 at the temperature T₀. Again, the heatexchange process can take place at a constant or near-constant pressuresuch that the working fluid exits the cold side CFX 2 at position 30 ata higher temperature but same pressure P₂, as indicated by P and T↓ atposition 30. Similarly, the temperature of the CTS medium 22 increasesin the cold side CFX 2, while its pressure can remain constant ornear-constant.

During discharge, the heat Q₂ is added to the CTS medium and the heat Q₁is removed from the HTS medium, wherein Q₁>Q₂. A net amount of work(W₂−W₁) is generated, since the work W₁ used by the compressor issmaller than the work W₂ generated by the turbine. A device thatgenerates work while moving heat from a hot body or thermal storagemedium to a cold body or thermal storage medium is a heat engine; thus,the thermal system in the discharge mode operates as a heat engine.

Another aspect of the disclosure is directed to thermal systems withregeneration/recuperation. In some situations, the terms regenerationand recuperation can be used interchangeably, although they may havedifferent meanings. As used herein, the terms “recuperation” and“recuperator” generally refer to the presence of one or more additionalheat exchangers where the working fluid exchanges heat with itselfduring different segments of a thermodynamic cycle through continuousheat exchange without intermediate thermal storage. As used herein, theterms “regeneration” and “regenerator” may be used to describe the sameconfiguration as the terms “recuperation” and “recuperator.” Theroundtrip efficiency of thermal systems may be substantially improved ifthe allowable temperature ranges of the storage materials can beextended. In some implementations, this may be accomplished by choosinga material or medium on the cold side that can go to temperatures below273 K (0° C.). For example, a CTS medium (e.g., hexane) with a lowtemperature limit of approximately T₀=179 K (−94° C.) may be used in asystem with a molten salt or solid HTS medium. However, T₀ ⁺ (i.e., thelowest temperature of the working fluid in the hot side heat exchanger)at some (e.g., modest) compression ratios may be below the freezingpoint of the molten salt, making the molten salt unviable as the HTSmedium. In some implementations, this can be resolved by including aworking fluid to working fluid (e.g., gas-gas) heat exchanger (also“recuperator” or “regenerator” herein) in the cycle.

FIG. 4 is a schematic flow diagram of working fluid and heat storagemedia of a thermal system in a charge/heat pump mode with a gas-gas heatexchanger 5 for the working fluid. The use of the gas-gas heat exchangercan enable use of colder heat storage medium on the cold side of thesystem. As examples, the working fluid can be air, argon, or a mixtureof primarily argon mixed with another gas such as helium. For example,the working fluid may comprise at least about 50% argon, at least about60% argon, at least about 70% argon, at least about 80% argon, at leastabout 90% argon, or about 100% argon, with balance helium.

FIG. 6A shows a heat storage charge cycle for the storage system in FIG.4 with a cold side storage medium (e.g., liquid hexane or heptane orsolid thermal medium) capable of going down to approximately to 179 K(−94° C.) and a molten salt or a solid thermal medium as the hot sidestorage, and η_(c)=0.9 and η_(t)=0.95. In some cases, the system caninclude more than four heat storage tanks.

In one implementation, during charge in FIGS. 4 and 6A, the workingfluid enters the compressor at T₁ and P₂, exits the compressor at T₁ ⁺and P₁, rejects heat Q₁, to the HTS medium 21 in the hot side CFX 2,exiting the hot side CFX 2 at T₁ and P₁, rejects heat Q_(recup) (also“Q_(regen)” herein, as shown, for example, in the accompanying drawings)to the cold (low pressure) side working fluid in the heat exchanger orrecuperator 5, exits the recuperator 5 at T₀ ⁺ and P₁, rejects heat tothe environment (or other heat sink) in section 38 (e.g., a radiator),enters the turbine 3 at {tilde over (T)}₀ ⁺ and P₁, exits the turbine atT₀ and P₂, absorbs heat Q₂ from the CTS medium 22 in the cold side CFX4, exiting the cold side CFX 4 at T₀ ⁺ and P₂, absorbs heat Q_(recup)from the hot (high pressure) side working fluid in the heat exchanger orrecuperator 5, and finally exits the recuperator 5 at T₁ and P₂,returning to its initial state before entering the compressor.

FIG. 5 is a schematic flow diagram of working fluid and heat storagemedia of the thermal system in FIG. 4 in a discharge/heat engine mode.Again, the use of the gas-gas heat exchanger can enable use of colderheat storage fluid or a solid medium (CTS) and/or colder working fluidon the cold side of the system.

FIG. 6B shows a heat storage discharge cycle for the storage system forthe storage system in FIG. 5 with a cold side storage medium (e.g.,liquid hexane or solid thermal storage medium) capable of going down to179 K (−94° C.) and a molten salt or a solid thermal storage medium asthe hot side storage, and ηc=0.9 and ηt=0.95.

During discharge in FIGS. 5 and 6B, the working fluid enters thecompressor at T₀ and P₂, exits the compressor at T₀ ⁺ and P₁, absorbsheat Q_(recup) from the cold (low pressure) side working fluid in theheat exchanger or recuperator 5, exits the recuperator 5 at T₁ and P₁,absorbs heat Q₁ from the HTS medium 21 in the hot side CFX 2, exitingthe hot side CFX 2 at T₁ ⁺ and P₁, enters the turbine 3 at {tilde over(T)}₁ ⁺ and P₁, exits the turbine at {tilde over (T)}₁ and P₂, rejectsheat to the environment (or other heat sink) in section 39 (e.g., aradiator), rejects heat Q_(recup) to the hot (high pressure) sideworking fluid in the heat exchanger or recuperator 5, enters the coldside CFX 4 at T₀ ⁺ and P₂, rejects heat Q₂ to the CTS medium 22 in thecold side CFX 4, and finally exits the cold side CFX 4 at T₀ and P₂,returning to its initial state before entering the compressor.

In some examples, recuperation may enable the compression ratio to bereduced. In some cases, reducing the compression ratio may result inreduced compressor and turbine losses. In some cases, the compressionratio may be at least about 1.2, at least about 1.5, at least about 2,at least about 2.5, at least about 3, at least about 3.5, at least about4, at least about 4.5, at least about 5, at least about 6, at leastabout 8, at least about 10, at least about 15, at least about 20, atleast about 30, or more.

In some cases, T₀ may be at least about 30 K, at least about 50 K, atleast about 80 K, at least about 100 K, at least about 120 K, at leastabout 140 K, at least about 160 K, at least about 180 K, at least about200 K, at least about 220 K, at least about 240 K, at least about 260 K,or at least about 280 K. In some cases, T₀ ⁺ may be at least about 220K, at least about 240 K, at least about 260 K, at least about 280 K, atleast about 300 K, at least about 320 K, at least about 340 K, at leastabout 360 K, at least about 380 K, at least about 400 K, or more. Insome cases, the temperatures T₀ and T₀ ⁺ can be constrained by theability to reject excess heat to the environment at ambient temperaturedue to inefficiencies in components such as turbomachinery. In somecases, the temperatures T₀ and T₀ ⁺ can be constrained by the operatingtemperatures of the CTS (e.g., a phase transition temperature). In somecases, the temperatures T₀ and T₀ ⁺ can be constrained by thecompression ratio being used. Any description of the temperatures T₀and/or T₀ ⁺ herein may apply to any system or method of the disclosure.

In some cases, T₁ may be at least about 350 K, at least about 400 K, atleast about 440 K, at least about 480 K, at least about 520 K, at leastabout 560 K, at least about 600 K, at least about 640 K, at least about680 K, at least about 720 K, at least about 760 K, at least about 800 K,at least about 840 K, at least about 880 K, at least about 920 K, atleast about 960 K, at least about 1000 K, at least about 1100 K, atleast about 1200 K, at least about 1300 K, at least about 1400 K, ormore. In some cases, T₁ ⁺ may be at least about 480 K, at least about520 K, at least about 560 K, at least about 600 K, at least about 640 K,at least about 680 K, at least about 720 K, at least about 760 K, atleast about 800 K, at least about 840 K, at least about 880 K, at leastabout 920 K, at least about 960 K, at least about 1000 K, at least about1100 K, at least about 1200 K, at least about 1300 K, at least about1400 K, at least about 1500 K, at least about 1600 K, at least about1700 K, or more. In some cases, the temperatures T₁ and T₁ ⁺ can beconstrained by the operating temperatures of the HTS. In some cases, thetemperatures T₁ and T₁ ⁺ can be constrained by the thermal limits of themetals and materials being used in the system. For example, aconventional solar salt can have a recommended temperature range ofapproximately 560-840 K. Various system improvements, such as, forexample, increased round-trip efficiency, increased power and increasedstorage capacity may be realized as available materials, metallurgy andstorage materials improve over time and enable different temperatureranges to be achieved. Any description of the temperatures T₁ and/or T₁⁺ herein may apply to any system or method of the disclosure.

In some cases, the round-trip efficiency η_(store) (e.g., electricitystorage efficiency) with and/or without recuperation can be at leastabout 5%, at least about 10%, at least about 15%, at least about 20%, atleast about 25%, at least about 30%, at least about 35%, at least about40%, at least about 45%, at least about 50%, at least about 55%, atleast about 60%, at least about 65%, at least about 70%, at least about75%, at least about 80%, at least about 85%, at least about 90%, or atleast about 95%.

In some implementations, at least a portion of heat transfer in thesystem (e.g., heat transfer to and from the working fluid) during acharge and/or discharge cycle includes heat transfer with theenvironment (e.g., heat transfer in sections 38 and 39). The remainderof the heat transfer in the system can occur through thermalcommunication with thermal storage media (e.g., thermal storage media 21and 22), through heat transfer in the recuperator 5 and/or throughvarious heat transfer processes within system boundaries (i.e., not withthe surrounding environment). In some examples, the environment mayrefer to gaseous or liquid reservoirs surrounding the system (e.g., air,water), any system or media capable of exchanging thermal energy withthe system (e.g., another thermodynamic cycle or system, heating/coolingsystems, etc.), or any combination thereof. In some examples, heattransferred through thermal communication with the heat storage mediacan be at least about 25%, at least about 50%, at least about 60%, atleast about 70%, at least about 80%, or at least about 90% of all heattransferred in the system. In some examples, heat transferred throughheat transfer in the recuperator can be at least about 5%, at leastabout 10%, at least about 15%, at least about 20%, at least about 25%,at least about 50%, or at least about 75% of all heat transferred in thesystem. In some examples, heat transferred through thermal communicationwith the heat storage media and through heat transfer in the recuperatorcan be at least about 25%, at least about 50%, at least about 60%, atleast about 70%, at least about 80%, at least about 90%, or even about100% of all heat transferred in the system. In some examples, heattransferred through heat transfer with the environment can be less thanabout 5%, less than about 10%, less than about 15%, less than about 20%,less than about 30%, less than about 40%, less than about 50%, less thanabout 60%, less than about 70%, less than about 80%, less than about90%, less than about 100%, or even 100% of all heat transferred in thesystem. In some implementations, all heat transfer in the system may bewith the thermal storage media (e.g., the CTS and HTS media), and onlythe thermal storage media may conduct heat transfer with theenvironment.

Thermal cycles of the disclosure (e.g., the cycles in FIGS. 4 and 5) maybe implemented through various configurations of pipes and valves fortransporting the working fluid between the turbomachinery and the heatexchangers. In some implementations, a valving system may be used suchthat the different cycles of the system can be interchanged whilemaintaining the same or nearly the same temperature profile across atleast one, across a subset or across all of counter-flow heat exchangersin the system. For example, the valving may be configured such that theworking fluid can pass through the heat exchangers in opposite flowdirections on charge and discharge and flow or conveyance directions ofthe HTS and CTS media are reversed by reversing the direction of thepumps or conveyance systems.

In some implementations, the system may be set up to enable switchingbetween different cycles. Such a configuration may be advantageous as itmay reuse at least a portion, or a substantial portion, or a majority,of the same piping and/or connections for the working fluid in both thecharging and discharging modes. While the working fluid may changedirection between charge and discharge, the temperature profile of theheat exchangers can be kept constant, partially constant, orsubstantially or fully constant, by changing the direction in which theHTS medium and the CTS medium are pumped or conveyed when switching fromcharge to discharge and vice-versa, and/or by matching the heat fluxesof the working fluid, the HTS medium and the CTS medium appropriately.

III. Illustrative Baffled Thermoclines in a Brayton Cycle Engine

FIG. 7 illustrates a Brayton cycle heat engine configured to generateelectrical power and supply such power to an electrical grid. The heatengine may be reversible (i.e., operate as a heat pump) and may take theform of other heat engines and/or reversible heat engines describeherein and may include additional or alternative components than thoseshown in the illustration. The heat engine may include a generator/motor701 that may generate electricity or use electricity to operate acompressor 703. The generator/motor 701 may be mechanically coupled tothe compressor 703 and a turbine 705. The compressor 703 and the turbine705 may be coupled to the generator/motor 701 via one or more shafts715. Alternatively, the compressor 703 and the turbine 705 may becoupled to the generator/motor 701 via one or more gearboxes and/orshafts. The heat engine may use mechanical work to store heat and/or mayprovide mechanical work from stored heat. The heat engine may have a hotside 717 and a cold side 719.

In one embodiment, the heat engine may include a hot-side thermoclinevessel 707 coupled between the compressor 703 and the turbine 705 on thehot side 717. The hot-side thermocline vessel 707 may act as adirect-contact heat exchanger, where a working fluid is in directcontact with a solid thermal medium and at greater than atmosphericpressure. An optional recuperative heat exchanger 711 may be disposed inthe working fluid path between the compressor 703 and the hot-sidethermocline vessel 707. With the use of the solid thermal medium, whichmay be effective across a wide temperature range, it may be possible toreduce or eliminate the use of a recuperative heat exchanger.

A cold-side thermocline vessel 709 may be coupled between the turbine705 and the compressor 703 on the cold side 719. The cold-sidethermocline vessel 709 may act as a direct-contact heat exchanger, wherea working fluid is in direct contact with a solid thermal medium and atless than atmospheric pressure, wherein the solid thermal medium on thecold side may be different than the solid thermal medium on the hotside. The recuperative heat exchanger 711 may be disposed in the workingfluid path between the turbine 705 and the cold-side thermocline vessel709, such that a working fluid stream downstream of the turbine 705 isin thermal contact with a working fluid stream downstream of thecompressor 703.

The hot-side thermocline vessel 707 and the cold-side thermocline vessel709 are preferably insulated pressure vessels. As used herein, apressure vessel is intended to refer to a vessel or containment areathat can operate at either or both above atmospheric pressure (e.g., 1to 5 bar, 5 to 30 bar, 30 to 100 bar, or greater) and/or belowatmospheric pressure (e.g., 1×10⁵ to 3×10³ Pa, 3×10³ to 1×10⁻¹ Pa,1×10⁻¹ to 1×10⁻⁷ Pa, or less). They may be insulated to prevent orreduce transmission of heat contained within the vessel to the externalenvironment. They may further be sealed to maintain the pressure ofincoming working fluid that may be substantially above or belowatmospheric pressure and to maintain a substantially isobaricenvironment where the working fluid may directly contact the solidthermal medium. The thermocline vessels 707 and 709 may include one ormore inlets for receiving the working fluid at non-atmospheric pressurefrom the closed thermodynamic cycle system, such as a Brayton cyclesystem, and one or more outlets for dispatching the working fluid atnon-atmospheric pressure to the closed thermodynamic cycle system. Theinlets and outlets may be one or more apertures through the exteriorwalls of the thermocline vessels 707 and 709 and that are connected tothe respective working fluid streams and sealed from the atmosphere.

The thermocline vessels 707 and 709 each preferably contain a solidthermal medium. The solid thermal medium may have a structure withporosity sufficient to allow the working fluid to flow through the solidthermal medium. The solid thermal medium may be segregated into aplurality of zones that are defined by a plurality of baffle structureswithin each pressure vessel. The baffle structures may be configured tolimit direct transfer of heat between the solid thermal medium indifferent zones, whether by conductive or radiative means. The bafflesmay have one or more fluid channels that allow the working fluid to flowpast the baffles and in contact (direct or thermal) with the solidthermal medium. The baffles may allow the thermocline vessels 707 and709 to maintain a thermocline within the vessel for an extended periodof time by reducing the transfer of heat from a hot side of thethermocline to the cold side of the thermocline. As an illustrativeexample, the thermocline in the hot-side thermocline vessel 707 mayexhibit a temperature difference of approximately 1500° C., 1400° C.,1300° C., 1200° C., 1100° C., 1000° C., 900° C., 800° C., 700° C., 600°C., 500° C., 400° C., 300° C., or 200° C. For example, the temperature(T_(h_high)) of the solid thermal medium near the outlet may beapproximately 1500° C., 1400° C., 1300° C., 1200° C., 1100° C., 1000°C., 900° C., 800° C., 700° C., 600° C. and the temperature (T_(h_low))of the solid thermal medium near the inlet may be approximately 200° C.or 100° C. As another example, the thermocline in the cold-sidethermocline vessel 709 may exhibit a temperature difference ofapproximately 400° C., 300° C., 200° C., or 100° C. For example, thetemperature (T_(c_high)) of the solid thermal medium near the inlet maybe approximately 200° C., 100° C., 70° C., 30° C. or 0° C. and thetemperature (T_(c_low)) of the solid thermal medium near the outlet maybe approximately −30° C., −100° C., or −200° C. Each of the thermoclinevessels may have one or more pressure sealed access ports to load orunload the solid thermal medium for thermal charging, maintenance, orother access requirements.

The heat engine illustrated in FIG. 7 may also have fluid pathsconfigured to allow it to operate without a recuperator (as in FIG. 2)and/or to operate reversibly and function to store excess electricalenergy in the form of thermal energy, similar to the cycle shown in FIG.4 or FIG. 1 (without a recuperator), where the hot side heat exchanger 2and associated tanks 6 and 7 and HTS medium 21 are replaced withthermocline 707 and the cold side heat exchanger 4 and associated tanks8 and 9 and CTS medium 22 are replaced with thermocline 709, and thefluid flow paths are as indicated in FIG. 1, 2 or 4. Due toinefficiencies likely present in the system, excess heat may need to berejected in the discharge or charge cycles. Heat rejection devices maybe inserted into the fluid paths of the described embodiments withoutdeparting from the claimed subject matter.

As an example embodiment only, in a discharge cycle, a heat rejectiondevice 713, such as a cooling tower, may be disposed in, or coupled to,the working fluid stream between the turbine 705 and the cold-sidethermocline vessel 709. The heat rejection device 713 may eject heatfrom the system, where the heat may be carried into the heat rejectiondevice 713 by the working fluid and ejected to the atmosphere or otherheat sink.

FIG. 8 illustrates a schematic arrangement, in cut-away view, of abaffled thermocline pressure vessel according to an example embodiment.The thermocline vessel 800 may include a pressure vessel 806 that isinsulated. The pressure vessel 806 may take various forms sufficient towithstand the pressure of the working fluid and to prevent or reduceheat transfer between the solid thermal medium and the externalenvironment. For example, the pressure vessel 806 may be a container.The outside walls of the container may include one or more materialsdesigned to withstand pressure and/or to minimize heat transfer. Forexample, the walls may include, internal insulation, an interior surfaceof refractory material, a structural steel core, and an externalinsulation and/or protective material capable of withstanding long-termenvironmental exposure. Pressure sealed access ports may be includedwithin the walls.

The thermocline vessel 800 may include an inlet 802 for working fluidfrom the Brayton cycle system and an outlet 804 for working fluid to theBrayton cycle system. The inlet 802 and outlet 804 may each be simplepipe ports with an opening into the interior of the pressure vessel 806and/or they may include more complex structures such as distributionplenums that connect to external piping containing the working fluid.

The thermocline vessel 800 may include baffle structures in one or moreconfigurations, such as baffle structures 808, 810, and 812. Each of thebaffle structures 808, 810, 812 may be an insulating wall and mayinclude fluid channels 814 that allow passage of working fluid past thebaffle structures. For clarity of the illustration in FIG. 8, only a fewof the fluid channels 814 are labeled. The fluid channels 814 may beapertures through the baffle structure 810. As illustrated in FIG. 8,the baffles 808, 810, 812 may extend completely across the thermoclinevessel 800. Baffle structure 814 may partially or completely define aninlet region 816 that may be filled with incoming working fluid from theinlet 802. Baffle structure 810 may include an arrangement of fluidchannels 814 that allows widespread distribution of the working fluidacross a span of the interior of the thermocline vessel 800. Forexample, baffle structure 810 may have more or less fluid channels 814or differently spaced or configured fluid channels 814 than other bafflestructures in the thermocline vessel 800. Similarly, baffle structure812 may partially or completely define an outlet region 818 that may befilled with incoming working fluid. Baffle structure 812 may include anarrangement of fluid channels 814 that allows widespread collection ofthe working fluid from across a span of the interior of the thermoclinevessel 800. For example, baffle structure 812 may have more or lessfluid channels or differently spaced or configured fluid channels thanother baffle structures in the thermocline vessel 800.

Baffle structures 808, together and/or in conjunction with bafflestructures 810, 812 may partially or completely define a plurality ofzones within the insulated pressure vessel 800. Each zone may contain asolid thermal medium 820. The baffle structures 808 are preferablyconfigured to limit direct transfer of heat between the solid thermalmedium 820 in different zones, such as conduction or radiation of heatbetween a bolus of the solid thermal medium in one zone and a bolus ofthe solid thermal medium in a different zone, while allowing passage ofa working fluid past the baffle structures and into contact with thesolid thermal medium 820.

In the thermocline vessel 800, each of the zones may contain the solidthermal medium 820 at a different temperature, forming a thermoclineconfiguration as illustrated in FIG. 8 by T₂ through T₈. A zoneproximate to the inlet (i.e., an “inlet zone”) may be at a temperatureT₂. A zone proximate to the outlet (i.e., an “outlet zone”) may be at adifferent temperature T₉. Each of the zones between the inlet zone andthe outlet zone may be at differing temperatures that form a gradientbetween T₂ and T₈. For example, in a hot-side thermocline vessel, thethermocline may take the form of T₉>T₈>T₇>T₆>T₅>T₄>T₃>T₂. As furtherillustration, the solid thermal medium 820 in the outlet zone may be atapproximately T₉=600° C. and the solid thermal medium 820 in the inletzone may be at approximately T₂=400° C. As another example, in acold-side thermocline vessel, the thermocline may take the form ofT₉<T₈<T₇<T₆<T₅<T₄<T₃<T₂. As further illustration, the solid thermalmedium 820 in the outlet zone may be at approximately T₉=−70° C. and thesolid thermal medium 820 in the inlet zone may be at approximatelyT₂=30° C.

FIG. 9 illustrates another schematic arrangement, in cut-away view, of abaffled thermocline pressure vessel according to an example embodiment.The thermocline vessel 900 illustrated in FIG. 9 is similar to theembodiment in FIG. 8 except that the baffle structures 908 do not extendcompletely across thermocline vessel 800, as illustrated in FIG. 8. Thebaffle structures 908 may be insulating walls and the fluid channels 914may be formed by spaces between the ends of the insulating walls and aninterior wall of the pressure vessel. The resulting serpentine flow pathfor the working fluid may provide a greater residence time for theworking fluid in the thermocline vessel 900 when compared to the moredirect flow path of the thermocline vessel 800.

FIG. 10 illustrates another schematic arrangement, in cut-away view, ofa baffled thermocline pressure vessel according to an exampleembodiment. The thermocline vessel 1000 is similar to the embodiments inFIGS. 8 and 9 except that the baffle structures 1008 are insulatedchambers which define zones for the solid thermal medium 820 within thechambers. Each of the baffle structures 1008 include one or more fluidchannels 1014 that allow a working fluid to enter the chambers andcontact the solid thermal medium 820. In one example, the bafflestructures 1008 may be formed as permanent constructions, for exampleswith walls of refractory brick or other materials with gaps or aperturesthrough the walls. In another example, the baffle structures 1008 may bemobile containers such as crucibles that may be placed into, removedfrom, or moved within the pressure vessel 806. Such an arrangement mayreduce the overall heat transfer between the working fluid and the solidthermal medium 820, but may have other benefits such as flexibility ofdesign, ease of maintenance, and/or recharging the thermal energy in thesystem.

FIG. 11 illustrates another schematic arrangement, in cut-away view, ofa baffled thermocline vessel with a runner system according to anexample embodiment. The thermocline vessel 1100 illustrated in FIG. 11is similar to the embodiment in FIG. 8 except that the working fluid isconfined within runners instead of flowing throughout the vessel 1106.Accordingly, vessel 1106 may be operable at atmospheric pressure. Theworking fluid may enter the vessel 1100 at inlet 1102, be distributedthrough a plenum 1116 to a series of runners 1122, enter a plenum 118,and exit the vessel 1100 at outlet 1104. The runners 1122 are configuredto allow heat to transfer between the solid thermal medium 820 and theworking fluid in the runners 1122. Heat transfer may be by conduction,convection (e.g., from an atmosphere within the vessel 1106), and/orradiative action. Preferably the runners 1122 are in direct contact withthe solid thermal medium, but they may be in non-direct thermal contactonly.

As an example only, the baffle structures 1108 may be insulating wallssimilar to those described with respect to FIGS. 8 and 9, except thatthe fluid channels 1114 are sized to allow the runners containing theworking fluid to pass the walls.

FIGS. 12 through 15 illustrate example embodiments of forms of bafflestructures inside a thermocline vessel, as viewed in a direction ofworking fluid flow. Each of the illustrations reflects implementation ina pressure vessel 806, but the example baffle structures could beimplemented in a non-pressurized thermocline vessel such as the runnersystem illustrated in FIG. 11. FIG. 12 illustrates a baffle structure1200 a where the fluid channels are apertures 1202 a between components1202 (e.g., bricks) used to construct the baffle structure. FIG. 13illustrates a baffle structure 1200 b where the fluid channels areapertures 1204 a through a perforated material 1204. FIG. 14 illustratesa baffle structure 1200 c where the fluid channels are gaps 1206 abetween components 1206 (e.g., slats or rods) used to construct thebaffle structure. FIG. 15 illustrates a baffle structure 1200 d wherethe fluid channel is a gap 1208 a between an interior surface of thepressure vessel 806 and the wall 1208.

Preferably the baffle structures 1200 a, 1200 b, 1200 c, and 1200 d haveinsulating properties to limit the conduction of heat from the solidthermal medium on one side of the structure to the solid thermal mediumon the other side of the structure. The fluid channels may be sized orlocated to limit or prevent the movement of the solid thermal mediumthrough the aperture. Alternatively or additionally, the fluid channelsmay be sized, located, and/or shaped to limit the passage of radiativeheat transfer. For example, a fluid channel may be smaller than a pelletof the solid thermal medium and/or a fluid channel may be angled orconvoluted in form such that there is no or limited line-of-sightbetween the solid thermal medium on one side of the baffle structure andthe solid thermal medium on the other side of the baffle structure.

VI. Conclusion

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

What is claimed is:
 1. An energy generation system, comprising: agenerator configured to receive mechanical energy and generateelectrical energy; a working fluid; a compressor configured to compressthe working fluid; a turbine configured to convert expansion of theworking fluid within the turbine into mechanical energy, wherein theturbine is mechanically coupled to the generator and is configured totransmit at least a portion of the mechanical energy to drive thegenerator; a hot-side thermocline vessel comprising a first plurality ofzones of a first solid thermal medium defined by first baffle structuresin an interior of the hot-side thermocline vessel, wherein the firstbaffle structures are configured to limit direct transfer of heatbetween the first solid thermal medium in different zones, wherein thefirst solid thermal medium within a first inlet zone proximate to aninlet of the working fluid to the hot-side thermocline vessel is at afirst temperature, and wherein the first solid thermal medium within afirst outlet zone proximate to an outlet of the working fluid from thehot-side thermocline vessel is at a second temperature different thanthe first temperature; and a cold-side thermocline vessel comprising asecond plurality of zones of a second solid thermal medium defined bysecond baffle structures in an interior of the cold-side thermoclinevessel, wherein the second baffle structure are configured to limitdirect transfer of heat between the second solid thermal medium indifferent zones, wherein the second solid thermal medium within a secondinlet zone proximate to an inlet of the working fluid to the cold-sidethermocline vessel is at a third temperature, and wherein the secondsolid thermal medium within a second outlet zone proximate to an outletof the working fluid from the second thermocline vessel is at a fourthtemperature different than the third temperature, and wherein theworking fluid circulates, in order, through (i) the compressor, (ii) thehot-side thermocline vessel in thermal contact with the first solidthermal medium, (iii) the turbine, and (iv) the cold-side thermoclinevessel in thermal contact with the second solid thermal medium.
 2. Theenergy generation system of claim 1, wherein the first plurality ofzones comprise one or more intermediate zones disposed between the firstinlet zone and the first outlet zone.
 3. The energy generation system ofclaim 2, wherein the first solid thermal medium in each of the one ormore intermediate zones is at a temperature between the firsttemperature and second temperature.
 4. The energy generation system ofclaim 1, wherein the magnitude of the difference between the firsttemperature and the second temperature is greater than 200° C.
 5. Theenergy generation system of claim 1, further comprising a heat rejectiondevice configured to eject from the energy generation system heatcarried by the working fluid.
 6. The energy generation system of claim1, wherein the working fluid within the hot-side thermocline vessel isat a pressure greater than atmospheric pressure.
 7. The energygeneration system of claim 1, wherein the working fluid within thecold-side thermocline vessel is at a pressure greater than atmosphericpressure.
 8. The energy generation system of claim 1 further comprisinga recuperative heat exchanger configured to thermally contact theworking fluid downstream from the compressor with the working fluiddownstream from the turbine, wherein the working fluid circulates, inorder, through (i) the compressor, (ii) the recuperative heat exchanger,(iii) the hot-side thermocline vessel in thermal contact with the firstsolid thermal medium, (iv) the turbine, (v) the recuperative heatexchanger, and (vi) the cold-side thermocline vessel in thermal contactwith the second solid thermal medium.
 9. The energy generation system ofclaim 8 further comprising a heat rejection device configured to ejectfrom the system heat carried by the working fluid, wherein the workingfluid circulates, in order, through (i) the compressor, (ii) therecuperative heat exchanger, (iii) the hot-side thermocline vessel inthermal contact with the first solid thermal medium, (iv) the turbine,(v) the recuperative heat exchanger, (vi) the heat rejection device, and(vii) the cold-side thermocline vessel and the second solid thermalmedium.